1. Field of the Invention
The invention relates to solvent extraction systems that operate on aqueous feed solutions of zirconium chloride to remove iron contaminants.
2. Description of the Prior Art
Zirconium and hafnium metals are conventionally obtained by complicated chemical processing of zircon sand involving initial chlorination of the sand to produce mixed zirconium/hafnium chlorides, which are separated by liquid-liquid extraction techniques in a solvent extraction plant.
Following seaparation of the chlorides, the production of nuclear grade zirconium metal requires the extraction of iron contaminant from the zirconium chloride solution that comes from the solvent extraction circuit. This is normally carried out by passing such zirconium choloride solution as normally contaminated with FeCl.sub.3, to the top of a packed iron-removal column (having two or three theoretical stages) for countercurrent flow relative to methyl isobutyl ketone (MIBK) as an extraction solvent that is fed into the column adjacent to its bottom. The ferric chloride is extracted into the MIBK, which exits the column adjacent to its top. The iron-free ZrOCl.sub.2 solution exists the column adjacent to its bottom. The iron-loaded MIBK solution is stripped of the iron contaminant by countercurrent contact with water, normally carried out in a second, packed, iron-wash column.
In this conventional procedure, water containing the FeCl.sub.3 is saturated with MIBK as it leaves the iron-wash column. The MIBK content is recovered from the water by steam that normally flows countercurrent to the water in a packed, steam-stripper column. The MIBK is separated from steam condensate by decantation and the water is used in the iron-wash column.
In addition to this iron extraction system, the solvent extraction plant utilizes a still for purifying the MIBK circulating in the main Zr/Hf separation system, which becomes contaminated with tar-like substances. Typically, about 5% of the total MIBK solvent flow is continually removed and distilled. The MIBK is recovered as an overhead product. The tars accumulate in the bottom of the still and are periodically tapped for disposal as a hazardous waste. The iron-free MIBK from the iron extraction system is passed into the still for further purification before being reused.